I spoke too soon. My head is going to explode soon!
I noticed an oddity on the order that eventually arrived by email (it talked about taking over an existing broadband connection rather than a new supply thereof), and so I called BT up to ask about it. The person I spoke to said the order was a mess, did not have the correct full address, didn't have any billing info, and would have failed to progress.
She then cancelled that order and we tried again. Except now it is 100% absolutely not FTTP. Only FTTC is available according to this sales rep. So I asked her to check again, and explained the sockets and what the other rep had said. But she was certain -- no FTTP. She also pointed out that the previous sales rep had made a huge mess of the order, so I should not trust what she said. (wow -- claws out, eh?).
And worse still, rather than an engineer arriving next week, now I can't get one for three weeks.
The stupidity doesn't stop there. I received an email saying that the hub for the cancelled order had gone out, then literally 1 minute later another email saying I had to return it.
It is one big dog's breakfast. Serves me right for thinking BT was most likely to get it right, which is why I chose them to start with.
Anyway, I've looked again for a Master socket and there isn't one. Nothing near the fuse box or anywhere else. There are only four "rooms" (inc bathroom) and two cupboards. There's nowhere else for it to be hidden.
I will get to the bottom of this or die trying....